Figure 2.Variation of peak temperature with respect to
power density in the device for different values of substrate
thickness.

AlGaN/GaN based high electron
mobility transistors (AG-HEMTs) are the strong candidates
for the high power and high frequency applications due to
the superior properties ofAlGaN/GaN hetero-structure such as
high carrier saturation velocity, wide band gap, high
breakdown field and thermal conductivity. However,
reliability concerns such as performance degradation at
elevated temperatures or stresses need to be addressed for
the widespread realization of AG-HEMTs. Understanding the
underlying details of the thermal transport in the device is
going to be an important step towards solving heat
dissipation and reliability challenges in these devices. We
develop a multi-scale diffuse-ballistic thermal transport
model of AG-HEMTs and investigate the hot spot formation and
energy transport from hot-spot. Device is studied under both
DC and AC operations to understand the heat dissipation
effects on device performance under realistic conditions.

Figure 5. Effect of lateral thermal
spreading on temperature profile of GaN layer. Figures on the
left side (a, c, e) correspond to total lateral dimension of
106.5 µm and figures on the right (b, d, f) correspond to 26.5
µm. Channel length in both cases is kept the same at 6.5 µm. The
epicenter of hot spot is located below the gate edge near drain.
Bottom of substrate layer is kept at 300 K. Clearly in case of
greater lateral dimensions temperature is lowered significantly
(e.g., nearly 90 K at drain bias of 6 V (e, f))